The present invention relates generally to mixers and cavitation devices that are used for processing heterogeneous and homogeneous fluids by the controllable formation of cavitation bubbles. Each cavitation bubble serves as an independent mini-reactor, and uses the energy released upon implosion of the bubble to quickly alter the fluids. The device finds application in chemical, pharmaceutical, fuel, food and other industries to prepare solutions, emulsions, and dispersions, and to improve mass and heat transfer processes.
More particularly, the present invention relates to the modification of complex fluids composed of many individual compounds and utilizes cavity implosion energy to improve the homogeny, viscosity, and/or other physical characteristics of the fluids by altering their chemical composition and converting compounds to obtain upgraded, more useful products.
It has been reported that elevated pressure and increased temperature and vigorous mixing supplied by either acoustic or hydrodynamic cavitation initiate and accelerate numerous reactions and processes. Enhancing the reaction and processes by means of the energy released upon the collapse of cavities in the flow has found application in a number of technologies that are used for upgrading, mixing, pumping, and expediting chemical conversions. While extreme pressure or tremendous heat can be detrimental, expensive and mechanically cumbersome the outcome of such controlled treatments is often highly beneficial.
Cavitation can be created in many different ways such as, for example, hydrodynamic, acoustic, laser-induced or generated by direct injection of steam into a sub-cooled fluid, which produces collapse conditions similar to those of hydrodynamic and acoustic cavitations (Young, 1999; Gogate, 2008; Mahulkar et al., 2008). The direct steam injection cavitation coupled with the acoustic cavitation exhibits up to 16 times greater efficiency as compared to acoustic cavitation alone.
The formation of bubbles in fluid is noticeable, when its temperature approaches the boiling point. If fluid is irradiated with ultrasound waves or processed in a hydrodynamic cavitation reactor with suitable velocity, the cavitation bubbles will form at a concentration of hundreds per milliliter. Their formation can be suppressed by increasing the pressure. The bubbles take up space normally occupied by fluid resisting the flow and increasing the pressure. If the cavitation bubbles relocate into a slow-velocity, high-pressure zone (reversed Bernoulli's principle), they will implode within 10−8-10−6 s. The implosion is accompanied by a sharp, localized elevation in both pressure and temperature, as much as 1,000 atm and 5,000° C. Such elevations in pressure and temperature result in the generation of local jet streams with 100 m/s velocities and higher (Suslick, 1989; Didenko et al., 1999; Suslick et al., 1999; Young, 1999).
The collapse of cavities is accompanied by shock waves, vigorous shearing forces, and a release of significant amounts of energy, which activates atoms, molecules and radicals located within the gas-phase bubbles and the atoms, molecules and radicals in the surrounding fluid. The release of energies accompanying the collapse initiates chemical reactions and processes and/or dissipates into the surrounding fluid. In many cases, the implosion is emission-free. Often it is followed by the emission of ultraviolet and/or visible light, which may induce photochemical reactions and generate radicals (Zhang et al., 2008). One disadvantage of extremely high pressure is extreme heat generation, which may become important if overheating is detrimental to product quality and safety.
The cavitation phenomenon is categorized by the dimensionless cavitation number Cv, which is defined as: Cv=(P−Pv)/0.5ρV2, where P is the recovered pressure downstream of the constriction, Pv is the vapor pressure of fluid, V is an average velocity of fluid at the orifice, and ρ is its density. The cavitation number at which cavitation begins is the cavitation inception number, Cvi. Cavitation ideally begins at Cvi=1, and a Cv<1 indicates a higher degree of cavitation (Gogate, 2008; Passandideh-Fard and Roohi, 2008). Another important term is the processing ratio, which corresponds to a number of cavitation events in a unit of flow. The effect of surface tension and size of cavities on the hydrostatic pressure is defined as follows: Pi=Po+2a/R, where Pi is the hydrostatic pressure, a is the surface tension, and R is the radius of the bubble. The smaller the bubble, the greater the energy released during its implosion.
Cavitation is more dramatic in viscous fluids. If, for example, oil moves at a high speed causing its pressure to drop below the vapor pressure of some hydrocarbon constituents, cavitation will occur. The cavitation separates the liquid-phase, high-boiling-point compounds and their particles suspended in liquid compounds from the entrapped gases, water vapor and vapors of the affected compounds. Small particulates and impurities serve as nuclei for the cavitation bubbles that may reach a few millimeters in diameter, depending on conditions.
Cavitation generated by sound waves in the sonic (20 Hz-20 KHz) or in the ultrasonic (>20 KHz) ranges does not offer an optimized method. The disadvantage of such methodology is its batch environment. Such methodology cannot be used efficiently in a continuous process, because the energy density and the residence time would be insufficient for high throughput. For instance, the intensity threshold of ultrasound cavitation in water is higher than 0.3 W/cm2. The sound wave cavitation technology suffers from other drawbacks as well. Since cavitation effect diminishes with an increase in distance from the radiation source, the treatment efficacy depends upon container size, i.e., lower efficacy with larger vessels. In addition, alterations in fluid are not uniform and can occur at certain high intensity locations, depending on the frequency and interference patterns of the sound waves.
Hydrodynamic cavitation does not require the use of a specific type of container as does sound or ultrasound-induced cavitation. Numerous flow-through hydrodynamic devices are known. See, for example, U.S. Pat. No. 6,705,396 to Ivannikov et al., and U.S. Pat. Nos. 7,207,712, 6,502,979 and 5,971,601 (Kozyuk), which describe different hydrodynamic cavitation reactors and their usage.
U.S. Pat. No. 7,338,551 to Kozyuk discloses a device and method for generating bubbles in a fluid that passes through a first local constriction of hydrodynamic cavitation device at a velocity of at least 12 m/s and then is mixed with gas to enhance implosion within the second cavitation field. Although, this device provides two cavitation zones, its efficiency is not satisfactory when a higher number of the consecutive cavitations is desired.
Another approach illustrated in the U.S. Pat. No. 5,969,207 to Kozyuk uses a flow-through passage accommodating a baffle body that generates a hydrodynamic cavitation with cavitation number (Cv) of at least 1 to initiate chemical transformations and to change the qualitative and quantitative composition of liquid hydrocarbons.
Russian Pat. No. 2143312, B 01 J 10/00 describes a gas-liquid system comprised of a vortex cavitation device surrounded by a vertical cylindrical housing. The cavitation device is positioned in the middle section of this housing and is equipped with both mixing and foam chambers coupled via a constricting nozzle. The feeding tube is coaxially aligned with the mixing chamber and functions as a cavitating nozzle with a conical splitter. In order to produce the swirl flow, the feeding tube has eight square threads with the openings separated by a 2-5 mm distance. The main disadvantages of this device are manufacturing complexity and high resistance to flow due to the swirling element.
Yet another Russian Pat. No. 2126117, F 24 J 3/00 discloses a heating cavitation device comprising a cylindrical housing, a Venturi-type nozzle and a baffle body, which is placed inside it. The Venturi-type nozzle houses a rotating impeller positioned in front of the baffle body along the flow. The outer surface of the baffle body has longitudinal slots that are amenable to the impeller and are coupled to the other end of the baffle body with the holes. The major drawback of said device is its manufacturing cost. Moreover, the impeller is prone to jamming, which decreases the treatment efficiency.
The patent of Russia No. 2158627, B 01 J 5/08 introduces a cavitation mixer comprising a cylindrical working chamber, a fluid feeding nozzle shaped as a convergent cone and a cone nozzle for discharging the atomized fluid. The chamber inlet houses a multi-jet nozzle for fluid mixing, which is followed by a nozzle for an optional introduction of additional components. The working chamber has a circular threshold-shaped runner attached to its interior. The inner surface of the chamber's rear end comprises the radial longitudinal ribs. This device is not capable of generating a uniform cavitation field within the chamber, and, as a result, the efficiency of processing is insufficient.
At the present time, with the cost of energy rising rapidly, it is highly desirable to shorten processing time and lower energy consumption to secure as large a profit margin as possible. The prior art techniques do not offer the most efficient method of upgrading fluids, especially complex mixtures and non-Newtonian viscous liquids in the shortest amount of time possible.
Therefore, need exists for an advanced flow-through device for mixture processing with a minimal treatment time and energy cost resulting in products with improved characteristics that can be easier to handle. The advanced, compact, and highly efficient device is particularly desired at the mining locations and refineries, where throughput is a key factor. The present invention provides such a device while delivering upgraded products within a short time.